Early IgG / IgA response in hospitalized COVID-19 patients is associated with a less severe disease

We determined the kinetics of anti-SARS-CoV-2 antibody response in fifteen hospitalized COVID-19 patients. Patients were divided into mild/moderate (mild, n=1; moderate, n=4) or severe (n=10) and virus-specific anti-Nucleocapsid IgM, anti-Spike IgG and anti-Spike IgA were measured in serial serum samples collected 0-15 days after hospital admission. Surrogate neutralization assays were performed by testing inhibition of ACE-2 binding to Spike. In three patients (2 severe and 1 moderate case), serum antibodies and T-cell memory were monitored six months after baseline. Although IgM response tended to appear first, patients affected by less severe disease were more prone to an early IgG/IgA response. Neutralization of Spike binding to ACE2 correlated with anti-Spike IgG and IgA. IgG and IgA antibody response persisted at the six months follow-up. A recall T-cell response to the Spike antigen was observed in two out of three patients, not related to disease severity.